Merge pull #1133: Full node guide: describe reducing bandwidth options

en/full-node.md

@@ -1396,5 +1396,93 @@ ask for help on sites like [SuperUser](http://superuser.com).
 We can't provide direct support, but if you see a way to improve these
 instructions, please [open an issue.](https://github.com/bitcoin-dot-org/bitcoin.org/issues/new)
 
+## Configuration Tuning
+
+This section contains advice about how to change your Bitcoin Core
+configuration to adapt it to your needs.
+
+There are two ways to change your configuration.  The first is to start
+Bitcoin Core with the options you want.  For example, if you want to
+limit it to using one CPU core for signature verification, you can start
+Bitcoin Core like this:
+
+{% highlight bash %}
+## Bitcoin Core daemon
+bitcoind -par=1 -daemon
+
+## Bitcoin Core GUI
+bitcoin-qt -par=1
+{% endhighlight %}
+
+Once you've decided you like an option, you can add it to the Bitcoin
+Core configuration file.  You can find that file in the following
+directories:
+
+- Windows: %APPDATA%\Bitcoin\
+
+- OSX: $HOME/Library/Application Support/Bitcoin/
+
+- Linux: $HOME/.bitcoin/
+
+To add an option to the configuration file, just remove its leading
+dash.  You may also need to remove any quotation marks you used in your shell.
+For example, the `-par` option seen above would look like this in the
+configuration file:
+
+{% highlight text %}
+par=1
+{% endhighlight %}
+
+If you have any questions about configuring Bitcoin Core, please stop by
+one of our [forums](/en/bitcoin-core/help#forums) or [live
+chatrooms](/en/bitcoin-core/help#live).
+
+### Reduce Traffic
+
+Some node operators need to deal with bandwith caps imposed by their ISPs.
+
+By default, bitcoin-core allows up to 125 connections to different peers, 8 of
+which are outbound. You can therefore, have at most 117 inbound connections.
+
+The default settings can result in relatively significant traffic consumption.
+
+Ways to reduce traffic:
+
+#### Maximum Upload Targets
+
+{% highlight text %}
+-maxuploadtarget=<MiB per day>
+{% endhighlight %}
+
+A major component of the traffic is caused by serving historic blocks to other nodes
+during the initial blocks download phase (syncing up a new node).
+This option can be specified in MiB per day and is turned off by default.
+This is *not* a hard limit; only a threshold to minimize the outbound
+traffic. When the limit is about to be reached, the uploaded data is cut by no
+longer serving historic blocks (blocks older than one week).
+Keep in mind that new nodes require other nodes that are willing to serve
+historic blocks. **The recommended minimum is 144 blocks per day (max. 144MB
+per day)**
+
+#### Disable listening
+
+{% highlight text %}
+-listen=0
+{% endhighlight %}
+
+Disabling listening will result in fewer nodes connected (remember the maximum of 8
+outbound peers). Fewer nodes will result in less traffic usage as you are relaying
+blocks and transactions to fewer nodes.
+
+#### Reduce maximum connections
+
+{% highlight text %}
+-maxconnections=<num>
+{% endhighlight %}
+
+Reducing the maximum connected nodes to a miniumum could be desirable if traffic
+limits are tiny. Keep in mind that bitcoin's trustless model works best if you are
+connected to a handful of nodes.
+
 </div>
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